These studies will characterize the toxicity and carcinogenic potential F344, rats and B6C3F1 mice associated with exposure to glyoxal in the drinking water. Prechronic toxicity will be evaluated by administering glyoxal at five different concentrations for 13 weeks. At the end of the study organ weights will be determined and all animals will receive a complete gross examination. Histopathological evaluation of all tissues with gross lesions and of target organs will be done. The carcinogenic potential of glyoxal will be evaluated by administering glyoxal at three different concentrations in drinking water to F344 rats and B6C3F1 mice for 2 years. At the end of the study all animals will receive a complete gross examination, all tissues will be saved fixed, and slides made. Histopathologic evaluation of all tissues in high dose and control animals and in target tissues in lower dose animals will be conducted.